Method to improve reliability of high-K metal gate stacks

ABSTRACT

A method of fabricating a gate stack for a semiconductor device includes the following steps after removal of a dummy gate: growing a high-k dielectric layer over an area vacated by the dummy gate; depositing a thin metal layer over the high-k dielectric layer; annealing the replacement gate structure in an ambient atmosphere containing hydrogen; and depositing a gap fill layer.

FIELD OF THE INVENTION

The invention disclosed broadly relates to the field of integratedcircuit fabrication, and more particularly relates to improving thereliability of high-k transistors using a replacement gate fabricationprocess.

BACKGROUND OF THE INVENTION

In the semiconductor industry, Moore's law states that the number oftransistors on a chip doubles approximately every two years. Theseexponential performance gains present a challenge to the semiconductormanufacturing industry, along with the dual challenges of promotingpower savings and providing cooling efficiency. The industry addressesthese challenges in multiple ways. Selecting the gate dielectric andgate electrode are critical choices in enabling device scaling, andcompatibility with CMOS technology. Two main approaches have emerged inhigh-k and metal gate (HKMG) integration: gate-first and gate-last.Gate-last is also called replacement metal gate (RMG) where the gateelectrode is deposited after S/D junctions are formed and the high-kgate dielectric is deposited at the beginning of the process (high-kfirst).

A high-k first gate-last process is when the high-k dielectric isdeposited first and the metal is deposited last (gate-last method).Gate-last is often referred to as the replacement gate option. “First”and “last”—gate denotes whether the metal gate electrode is depositedbefore or after the high temperature anneal process. Typically,reliability of high-k gate stacks improve as a result of dopantactivation anneal at temperatures around 1000° C., which is built in forgate-first or high-k first gate-last processes. The high-k lastgate-last (replacement gate) process, However, lacks such built-in hightemperature treatment, and thus reliability is a big challenge.

Referring now in specific detail to the drawings, and particularly toFIGS. 1A and 1B, there is provided a simplified pictorial illustrationof the gate fabrication process using a hydrogen (H2) anneal, accordingto the known art. Hydrogen gas is favored for its gate oxidereliability. FIG. 1A shows H2 150 annealed directly on a high-k layer110. The problems with this process are twofold: 1) the formation ofoxygen vacancies in the high-k dielectric 110; and 2) an undesired Vtshift, causing gate leakage degradation.

In FIG. 1B we provide a simplified illustration of another gatefabrication process using an H2 anneal 150 on a full structure with areplacement gate 130 in place, according to the known art. In thismethod, the supply of hydrogen is blocked by the metal layers. Moreover,the degree of interface passivation depends on the device size (largedevices can be un-passivated).

We provide a glossary of terms used throughout this disclosure:

Glossary.

k—dielectric constant value

high-k—having a “k” value higher than 3.9 k, the dielectric constant ofsilicon dioxide

CMOS—complementary metal-oxide semiconductor

FET—field effect transistor

FinFET—a fin-based, multigate FET

MOSFET—a metal-oxide semiconductor FET

CMP—chemical/mechanical polishing

Dit—interface states

RTA—rapid thermal anneal

HfO2—hafnium oxide

H2—hydrogen

D2—deuterium

A-Si—amorphous silicon

ALD—atomic layer deposition

PVD—physical vapor deposition

SiOx—silicon oxide

SiGe—silicon germanide

SiC—silicon carbide

RIE—reactive ion etching

ODL—optically dense layer; organically dielectric layer

STI—shallow trench isolation

S/D—source and drain terminals

NiSi—nickel silicide

C (DLC)—metal-free diamond-like carbon coating

SiN—silicon nitride

TDDB—time dependent dielectric breakdown

NBTI—negative bias temperature instability

PBTI—positive bias temperature instability

RTA—rapid thermal annealing

IL/HK—interfacial layer/high-k dielectric layer

TiN—titanium nitride

TiC—titanium carbide

TaN—tantalum nitride

TaC—tantalum carbide

TiAl—titanium aluminide

N2—nitrogen

Al—aluminide

W—tungsten

HfO2—Hafnium-based high-k dielectric

SUMMARY OF THE INVENTION

Briefly, according to an embodiment of the invention a method offabricating a gate stack for a semiconductor device includes thefollowing steps performed after removal of a dummy gate. Providing areplacement gate structure includes: growing a high-k dielectric layerover an area vacated by the dummy gate; depositing a thin metal layerover the high-k dielectric layer; annealing the replacement gatestructure in an ambient atmosphere containing hydrogen; and depositing agap fill layer.

According to another embodiment of the present invention a method offabricating a gate stack for a semiconductor device includes thefollowing steps performed after removal of a dummy gate. Providing areplacement gate structure includes: growing a high-k dielectric layerover an area vacated by the dummy gate; depositing a thin metal layerover the high-k dielectric layer; annealing the replacement gatestructure in an ambient atmosphere containing hydrogen; removing thethin metal layer after annealing; depositing a metal layer of lowresistivity metal; and depositing a gap fill layer.

According to an embodiment of the invention a method of fabricating agate stack for a FinFET device includes the following steps performedafter removal of a dummy gate. Providing a replacement gate structureincludes: growing a high-k dielectric layer over an area vacated by thedummy gate; depositing a thin metal layer over the high-k dielectriclayer; annealing the replacement gate structure in an ambient atmospherecontaining hydrogen; and depositing a gap fill layer.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

To describe the foregoing and other exemplary purposes, aspects, andadvantages, we use the following detailed description of an exemplaryembodiment of the invention with reference to the drawings, in which:

FIGS. 1A and 1B show schematics for conventional methods of H2 anneal onRMG devices;

FIGS. 2A through 2F show a gate structure undergoing the replacementgate process, according to an embodiment of the present invention;

FIGS. 3A through 3D show a gate structure undergoing the replacementgate process, according to another embodiment of the present invention;

FIG. 4 is a flowchart of a method according to an embodiment of theinvention;

While the invention as claimed can be modified into alternative forms,specific embodiments thereof are shown by way of example in the drawingsand will herein be described in detail. It should be understood,however, that the drawings and detailed description thereto are notintended to limit the invention to the particular form disclosed, but onthe contrary, the intention is to cover all modifications, equivalentsand alternatives falling within the scope of the present invention.

DETAILED DESCRIPTION

Before describing in detail embodiments that are in accordance with thepresent invention, it should be observed that the embodiments have beenrepresented where appropriate by conventional symbols in the drawings,showing only those specific details that are pertinent to understandingthe embodiments of the present invention so as not to obscure thedisclosure with details that will be readily apparent to those ofordinary skill in the art having the benefit of the description herein.Thus, it will be appreciated that for simplicity and clarity ofillustration, common and well-understood elements that are useful ornecessary in a commercially feasible embodiment may not be depicted inorder to facilitate a less obstructed view of these various embodiments.

We discuss a gate-last, high-k metal gate fabrication with a novelimprovement in reliability. We achieve this reliability by incorporatinghydrogen (H2) only in the thin metal and the high-k layer. Additionally,the H2 remains in the final film. We perform a passivation anneal withambient H2 after the thin metal deposition. Our anneal process isperformed at temperatures of 600 to 700 C on thin metal (TiN, TiC, TaN,TaC). The metal's thickness is between 10 and 50 angstroms. Thisfabrication method can be advantageously implemented in various CMOSdevices, including FinFET devices. We use only an intermediate thermaltreatment after dopant activation. This removes any dopant activation orS/D junction diffusion concerns.

Referring now to FIGS. 2A through 2F, we describe a gate-last, high-kmetal gate. FIG. 2A we show the gate structure 200 after removal of thedummy (sacrificial) gate. We grow an interfacial layer and deposit ahigh-k dielectric 110. In FIG. 2B, we show the gate structure 200 afterdeposition of a gate metal layer 120. The gate metal layer 120 in thisembodiment is a thin metal layer with a thickness of approximately 10 to50 angstroms. It is preferably a thermally stable metal alloy, such asTiN, TiC, TaN, or TaC. The gate metal layer 120 can be deposited viaatomic layer deposition (ALD) or physical vapor deposition (PVD). Afterdeposition of the thin metal layer 120, we follow with an anneal in anambient atmosphere containing H2 at 600-700 C.

In FIG. 2C we show an optional step of removing the thin metal layer 120after it has been annealed in H2 150. After optionally removing the thinmetal layer 120 we follow with deposition of a work function metal 140.This is shown in FIG. 2D. The work function metal 140 can be a metalalloy, such as TiAl or TiN. It serves the purpose of setting thethreshold voltage of the device to appropriate values. In FIG. 2E weshow the gate structure 200 after deposition of a gap fill metal 145 tofinish the replacement gate 200. The gap fill metal 145 can be Al, or W.Lastly, in FIG. 2F we show the gate structure 200 after performingchemical/mechanical polishing (CMP), a planarization process.

Referring now to FIGS. 3A through 3D we describe another gate-last,high-k metal gate with a novel improvement in reliability. In FIG. 3A,just as in FIG. 2A, we show the gate structure 300 after removal of thedummy (sacrificial) gate. We grow an interfacial layer and deposit ahigh-k dielectric 110. In FIG. 3B, we show the gate structure 200 afterdeposition of a gate metal layer 120. The gate metal layer 120 in thisembodiment is a thin metal layer 120 with a thickness of approximately10 to 50 angstroms. It is preferably a thermally stable metal alloy,such as TiN, TiC, TaN, or TaC.

The gate metal layer 120 can be deposited via atomic layer deposition(ALD) or physical vapor deposition (PVD). After deposition of the thinmetal layer 120, we follow with an anneal in an ambient atmospherecontaining H2 at 600°-700° C. The H2 anneal with the presence of thethin metal layer 120 enables a direct supply of active H species to theinterface while suppressing reduction of HfO2. We show a reliabilityimprovement without degradation in the effective work function and gateleakage current.

In FIG. 3C we show the gate structure 300 after deposition of a gap fillmetal 145 to finish the replacement gate 300. The gap fill metal 145 canbe Al, or W. Lastly, in FIG. 3D we show the gate structure 300 afterperforming chemical/mechanical polishing (CMP), a planarization process.

We will now discuss the process steps for gate last high-k gatefabrication with respect to the flowcharts of FIG. 4. Optional steps aredepicted in dotted boxes. It will be apparent to those with knowledge inthe art that the fabrication of a gate stack on a semiconductor deviceinvolves more steps than are shown in FIG. 4. For example, we skip overthe source/drain junction formation and show the process after the dummygate has been removed. For clarity, we concentrate our explanation onthose steps that deviate from the conventional fabrication of the high-kgate.

Referring now to FIG. 4, we show a flowchart 400 of the process forfabricating a gate-last high-k metal gate according to the embodiment ofFIGS. 2A through 2F. In step 410 we grow an interfacial layer anddeposit a high-k metal 110 after the dummy gate removal. In step 420 wedeposit the gate metal layer 120. This is followed by an H2 anneal at arange of 600° C. to 700° C. in step 430.

Next, we can optionally remove the thin metal layer 120 in step 440. Ifwe remove the metal 120 in step 440, then in step 450 we deposit a workfunction setting metal. Next, we deposit a gap fill metal 140 of lowresistivity in step 460 and finish with CMP planarization in step 470.The benefits and advantages to this embodiment are:

1. Enables a direct supply of active H species to the interface whilesuppressing reduction of HfO2.

2. Reliability improvement without degradation in the effective workfunction and gate leakage current.

Therefore, while there has been described what is presently consideredto be the preferred embodiment, it will understood by those skilled inthe art that other modifications can be made within the spirit of theinvention. The above description(s) of embodiment(s) is not intended tobe exhaustive or limiting in scope. The embodiment(s), as described,were chosen in order to explain the principles of the invention, showits practical application, and enable those with ordinary skill in theart to understand how to make and use the invention. It should beunderstood that the invention is not limited to the embodiment(s)described above, but rather should be interpreted within the fullmeaning and scope of the appended claims.

What is claimed is:
 1. A method of fabricating a gate stack for asemiconductor device, said method comprising steps of: growing a gatedielectric layer over an area vacated by a dummy gate being removed;depositing a first metal layer comprising at least one of TiN, TaN, TiC,and TaC on the gate dielectric layer; annealing the replacement gatestructure in an ambient atmosphere containing hydrogen gas after saiddepositing the first metal layer removing the first metal layer afterthe annealing step; depositing a second metal layer of low resistivitymetal; and depositing a gap fill layer over the annealed replacementgate structure.
 2. The method of claim 1 wherein the annealing isperformed at a temperature range of 600° C.-700° C.
 3. The method ofclaim 1 wherein depositing the second metal layer of low resistivitymetal comprises: depositing a work function metal; and depositing a gapfill metal of low resistivity.
 4. The method of claim 1 whereindepositing the first metal layer comprises depositing a thermally stablemetal alloy.
 5. The method of claim 4 wherein depositing the thermallystable metal alloy comprises deposition by atomic layer deposition. 6.The method of claim 5 wherein depositing the thermally stable metalalloy comprises deposition by physical vapor deposition.
 7. The methodof claim 1 further comprising: performing chemical mechanical polishing.8. A method of fabricating a gate stack for a semiconductor device, saidmethod comprising steps of: depositing a first metal layer comprising atleast one of TiN, TaN, TiC, and TaC over a gate dielectric layer;annealing the replacement gate structure in an ambient atmospherecontaining hydrogen gas after said depositing the first metal layer;removing the first metal layer after the first metal layer has beenannealed during said annealing the replacement gate structure;depositing a second metal layer of low resistivity metal on the gatedielectric layer of the annealed replacement gate structure; anddepositing a gap fill layer over the second metal layer.
 9. The methodof claim 8 wherein the annealing is performed at a temperature range of600° C.-700° C.
 10. The method of claim 9 wherein depositing the secondmetal layer of low resistivity metal comprises: depositing a workfunction metal; and depositing a gap fill metal of low resistivity. 11.The method of claim 10 wherein depositing the second metal layer of lowresistivity metal comprises depositing a thermally stable metal alloy.12. The method of claim 11 wherein depositing the thermally stable metalalloy comprises deposition by atomic layer deposition.
 13. The method ofclaim 12 wherein depositing the thermally stable metal alloy comprisesdeposition by physical vapor deposition.
 14. The method of claim 8further comprising performing chemical mechanical polishing.
 15. Amethod of fabricating a gate stack for a FinFET device, said methodcomprising steps of: growing a gate dielectric layer on a channel regionof a fin structure; depositing a first metal layer comprising at leastone of TiN, TaN, TiC, and TaC over the dielectric layer; annealing thereplacement gate structure in an ambient atmosphere containing hydrogengas after said depositing the first metal layer; removing the firstmetal layer after the annealing step; depositing a second metal layer oflow resistivity metal; and depositing a gap fill layer over the annealedreplacement gate structure.
 16. The method of claim 15 wherein theannealing is performed at a temperature range of 600° C.-700° C.
 17. Themethod of claim 15 wherein depositing the first metal layer comprisesdepositing a thermally stable metal alloy.
 18. The method of claim 15wherein depositing the thermally stable metal alloy comprises depositionby atomic layer deposition.
 19. The method of claim 15 whereindepositing the thermally stable metal alloy comprises deposition byphysical vapor deposition.
 20. The method of claim 15 further comprisingchemical mechanical planarization.